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 This invention relates to a receptacle for sampling fluid in a well bore, and to a method of obtaining a fluid sample. In particular, this invention relates to a receptacle having sensors which can monitor chemical and physical properties of the sample.
 Sampling of fluids within a well bore is becoming increasingly important as evaluation and development of a reservoir depends on the properties of the fluid in the reservoir. Downhole samples of the fluid are preferred to samples taken at the surface as they better represent downhole fluid properties. Fluid samples taken at the surface can have significantly different properties to a downhole sample due to variations in temperature and pressure that occur as the fluid travels to the surface and at the surface. Existing tools for downhole fluid sampling include a wireline conveyed sampling bottle which acquires a single sample downhole and is retrieved from downhole to surface. Wireline (coil tubing run) tools which are capable of pumping fluids from a borehole and from a reservoir formation into sampling chambers can also be used.
 Once samples have been taken and placed within a sample bottle, the subsequent transport of the sample to a laboratory can cause irreversible changes in the sample which will alter its properties, and limit its usefulness in assessing actual downhole properties of the reservoir fluid. For example, often the sample is transferred from a sample bottle to another suitable container for transport. Variations in conditions surrounding the container during transport will affect the sample and its properties. Also the sample must be transferred out of the container once the laboratory is reached and again this can affect the sample.
 The present invention aims to provide an apparatus and method for sampling fluid in a well bore.
 According to the invention an apparatus is provided for analysing fluid from a subterranean formation, the apparatus comprising a chamber adapted for deployment in a wellbore and to enclose and hold a sample of fluid; and a sensor adapted to sense at least one characteristic of fluid within the chamber while downhole.
 As used herein the term “fluid” refers to either gas or liquid.
 A communication means is preferably placed within a wall of the chamber so as to provide an externally accessible port which communicates with the inside of the chamber, but yet is sealed so as to ensure the seal of the chamber is not compromised. Communication can be carried out in various methods, for example via a cable (cable port) for real-time down hole or surface exchange. Alternatively a plug in port (or and remotely interrogated port) could be used. Alternatively, optical windows can be used for visual inspection.
 The chamber preferably further comprises a fluid conduit sealable by the sealing means, such as first and second valves placed at either end of the conduits and which open to allow fluid to pass through the chamber, and are shut to seal the chamber after a suitable sample has been acquired. Sometimes the downhole fluid is contaminated, for example with drilling mud, and in the contaminated state does not truly represent the characteristics of fluid from a reservoir of interest. Having a fluid conduit allowing through flow of fluid allows a sample to be selected once non-contaminated fluid is flowing through the chamber. Typically the sensing means actively samples the fluid properties to determine when there is no contamination present, at which point the valves are closed to trap a sample within the chamber.
 According to another embodiment, the fluid flows through a separate chamber, external to the bottle, where the contamination is assessed prior to filling the sample collection vessel. The vessel can also be used as a downhole PVT laboratory in this case the sample would be collected, analysed and expunged before returning the tool to surface empty. Thus a type of emission free testing can be provided.
 The apparatus may include a plurality of sensors each capable of detecting and analysing a characteristic of the sample. Thus the apparatus may comprise sensors which detect and analyse temperature, pressure, physical properties and chemical properties of the sample.
 The chamber may further comprise means for altering pressure and means for altering temperature, where the communication means monitors temperature and pressure readings from the sensing means and adjusts the means for altering pressure and the means for altering temperature to keep pressure and temperature constant within the chamber. Typically the means for altering pressure is a piston within the chamber which alters the volume of the chamber as it moves to control pressure, with the means for altering temperature being a heating coil either external or internal to the chamber. The communication means is thus able to monitor and actively control the conditions within the chamber to ensure that the conditions under which the sample was acquired are maintained continuously, even after the receptacle is brought to surface from downhole. This ensures that the sample does not undergo irreversible changes relating to its characteristics as a result of subsequent changes in the temperature of the receptacles surrounding and thus pressure.
 The apparatus may be adapted to be remotely interrogated so as to allow for information transfer and monitoring of conditions inside the chamber during transport of the receptacle and during storage of the receptacle.
 The apparatus may also include a connector to connecting to a wireline. This allows the chamber to be lowered downhole on a wireline for collection of a sample and subsequently retrieved to surface.
 The chamber may comprise a plurality of modules in mating engagement with the chamber, the modules containing analytical and processing equipment for analysis of a sample. By having an apparatus which is assembled from a series of modules and a chamber, the apparatus can be readily modified for different types of analysis as each module performs a different type of interaction with the sample in the main chamber. Thus, for example, the apparatus may comprise a main chamber with three minor compartments disposed at a lower end of the chamber and two further minor compartments disposed at an upper end of the chamber, the five minor compartments respectively containing analytical equipment, chemicals, sample treatment chamber, a spectrometer with a light source, and electronic processing devices. The apparatus may also have a means of varying the pressure such as a moveable piston.
 The apparatus preferably communicates with a memory device to store information relating to the sample as a function of time for subsequent download. The memory device may be contained in a module attached to the chamber.
 The chamber typically includes means for altering pressure and temperature and sensing means so that a self-contained unit is provided for holding the sample. The minor compartments or modules may contain chemicals for injecting into the main chamber when needed, with this injection being regulated by the communication means. These chemicals may be appropriate for removing gases such as H
 The apparatus may further comprise a stirring device located within the chamber, such as an acoustic transducer.
 The chamber may be provided with optical windows within its walls, such as made of sapphire so that the contents of the chamber can be viewed when needed.
 The receptacle thus provides integral sampling and analysis within one vessel and ensures that no transfer of sample outside the chamber is needed for analysis to take place. Thus a simple, small tool is provided which is particularly suitable for use downhole.
 In accordance with another aspect of the invention, there is provided a method of sampling downhole fluids, comprising placing a chamber downhole; collecting at least one sample in the chamber; sealing the sample within the chamber; sensing at least the temperature and pressure of the sample in the chamber; and controlling the temperature and pressure of the sample in response tot he sensed temperature and pressure.
 The invention will now be described, by way of example, and reference to the accompanying drawings in which:
 With conventional sampling bottles, the sample is transferred at least once before analysis of the sample is undertaken and the conditions within the chamber cannot be monitored or maintained during transport or storage of the sample. The sample bottle in accordance with the present invention preferably allows monitoring of the physical and chemical parameters of the sample in the chamber whilst undergoing transport, and allows testing of the physical and chemical properties of the sample in situ within the chamber without exposure of the sample to conditions different to those downhole.
 The receptacle, or sampling bottle, is capable of replicating and maintaining equivalent downhole conditions in an internal chamber where the sample is held, as discussed later. This ensures that once the sample is taken, it is kept stable at downhole conditions and physical and chemical changes that might occur to the sample during the trip to the surface and to a laboratory are prevented. The sample when analysed thus more accurately reflects the properties of downhole fluid.
 The physical and chemical properties of the fluid which are of interest when assessing the reservoir include viscosity, density, bubble and dew point, wax, asphaltene, scale precipitation conditions, hydrate formation, chemical composition. It is important to avoid physical and chemical changes to the sample as many of these changes are irreversible or effectively irreversible, and will alter the sample properties. Effectively irreversible changes are those which in principle are thermodynamically irreversible but the kinetics of achieving equilibrium are so slow that it is not practical to reverse the change fully.
 Where irreversible or effectively irreversible changes have occurred to the sample before analysis, the initial chemical and physical state of the sample, i.e. as in the reservoir, will generally not be precisely reconstructed even if the sample is put under reservoir temperature and pressure conditions during analysis. The sample properties will then not reflect downhole fluid properties. Hence, for practical purposes it is always best to avoid any chemical or physical changes to the fluid sample prior to analysis whether the change is considered to be reversible or not. Examples of various changes that can occur with reservoir fluids are summarized below:
 1. Organic solids precipitation, for example asphaltenes and waxes, due to pressure and temperature drop;
 2. Degassing of a sample, for example, arising from the (fluid) liquid pressure falling below the bubble pressure and the evolved gas escaped, perhaps through a seal;
 3. Mineral precipitation (barite, calcite) due to temperature and/or pressure drop and degassing;
 4. Loss of gases (mainly H
 5. Formation of gas hydrates;
 6. Vapour-liquid phase separation;
 7. Changes in pH; and
 8. Other chemical and physical changes.
 The cylindrical sampling bottle of around 1 m in length is shown in detail in
 Towards the base of vertical walls
 In one vertical wall
 A piston
 Power is supplied to the connector
 Any particular combination of sensors and equipment can be used within the chambers
 Some chemical sensors and miniaturized chemical analytical equipment (for example, Gas Chromatography (GC), liquid chromatography (LC), and mass spectrometry (MS)) are not in direct contact with the sampled fluid as they require sample preparation, but are held in the minor modules
 The various chemical sensors and chemical analytical equipment allow the following properties and information to be determined:
 (i) Determine downhole sample chemistry needed for real-time reservoir evaluation.
 (ii) Provide information for downhole sample validation. Thus the bottle allows contamination to be measured and this can be used to determine when the sample should be taken. Reservoir fluid is either continuously pumped through the chamber or intermittently sampled for these measurements.
 (iii) Record the evolution of a sample containment conditions and in-bottle chemistry during the trip to the surface and to the laboratory.
 (iv) Provide extra analytical possibilities on-rig on the surface and in the laboratory as extra modules with different chemical sensors/analytical equipment can be placed in communication with the main chamber
 Where appropriate, specific chemicals are introduced into the chamber
 (i) Absorb/remove aggressive gases (for example H
 (ii) Provide an acidification to avoid mineral (for example carbonate) precipitation.
 (iii) Inhibit mineral (barite) precipitation.
 (iv) Calibrate chemical sensors. The bottle can be filled by a calibration solution to check sensors performance before being placed downhole
 (v) Calibrate physical sensors, for example density sensors.
 Other sensors that can be used include acoustic transducers and acoustic sources to determine fluid phase transition and physical properties, such as bubble and dew point, wax and asphaltenes deposition. These sensors can be placed in the piston or in the wall of the chamber, or as a changeable, plug-in module. Acoustic measurements such as speed and attenuation of sound can be used for density and viscosity measurements.
 Stirring devices
 Vibrating objects
 The memory block
 In step
 In step
 Thus, the bottle is used to monitor continuously wellbore and reservoir (formation) fluid properties and the amount of contamination of the fluid with drilling mud. The bottle can also be used for zero-emission testing.
 Referring again to
 As the sample is hermetically sealed within the main chamber and testing is possible without interfering with the seal, the sample integrity is maintained indefinitely. In step
 In use, the chamber
 Instead of taking one sample and retrieving the bottle
 When used in a flow through mode, or a multi-sample mode, the system can be used for emission free testing with a down hole drill stem tester (DHDST) or a modular formation dynamic tester (MDT).
 In step
 At surface, the actions and analyses carried out upon the sample
 During surface transfer of the bottle from the rig to the laboratory (step
 According to another embodiment of the invention, the bottle is used simply to convey samples from surface at a well to a laboratory.
 The bottle thus has a variety of different applications. In its more general form it provides a mini portable modular chemical/physical laboratory which allows analysis of a sample anywhere, avoiding the need to take the sample to a laboratory before analysis is undertaken.
 The bottle can also act as an integrated transport and analysis vessel, when a sample is placed into the chamber when on surface. The bottle then monitors, records and controls sample conditions and analyses the sample during transport and/or storage.
 In addition the bottle can act as an integral unit that acquires a sample, analyses a sample both downhole and on surface, and is a transport vessel. This ensures that a sample can be acquired, analysed and transported without any sample transfer between different containers. The sample integrity is thus maintained for as long a period as desired.
 The above-described embodiments are illustrative of the invention only and are not intended to limit the scope of the present invention.